Light emitting diodes (LEDs) emit light when voltages are applied across their P/N junctions. Characteristics of LEDs such as their optical performance and operating life are a function of temperature across the P/N junctions. For example, a wavelength of emitted light changes as the junction temperature rises. Accordingly, LEDs and their junction temperature are cooled to optimize the optical performance of the LEDs. Traditional methods of LED cooling include using passive cooling devices such as heat slugs or heat sinks to dissipate heat. These methods rely on either cooling of LED heat source using heat conduction through devices having a lower thermal resistance to other parts of the LED, or using heat convection from the heat source or the passive cooling devices to ambient air.
While passive cooling devices are widely used to cool LEDs, the efficiency of heat transfer using these devices has not been entirely satisfactory. For example, the amount of heat transfer in convective heating is a function of the temperature difference between the heat source and the ambient air. As the ambient air temperature heats up from the convective heating, the efficiency of heat transfer decreases. In addition, in conductive heating, semiconductor materials and other materials used to provide the thermal path in the LEDs may have poor thermal conductivity, resulting in poor heat conduction. Furthermore, it is difficult to control the junction temperature of LEDs within a desirable range for optimum optical performance when passive cooling devices are used. Accordingly, there is a need for methods of LED cooling that have high heat transfer efficiency while allowing the junction temperature of LEDs to be more accurately controlled.
Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.